design and optimization of an esu for hybrid light vehicles with the use of supercapacitors...

Design and Optimization of Design and Optimization of an ESU for hybrid light an ESU for hybrid light vehicles with the use of vehicles with the use of

SupercapacitorsSupercapacitors

Students:Aniello ValentinoFrancesco Villella

Supervisor:Stefano CarabelliMarcello Chiaberge

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IndexIndex

Introduction Supercapacitor ESU with Supercapacitors DC/DC Converter Modeling Results Conclusions

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IndexIndex


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IntroductionIntroduction

Context

Motivations

Objectives

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ContexContexESU with add-on Supercapacitors

TTW Three Tilting Wheels

IntroductionContext

The Supercapacitors are an addition to batteries they can be inserted or excluded depending on the needs.

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MotivationsMotivations Use supercapacitors in parallel with the battery to improve

acceleration and energy recovery during braking Designed for peak power requirements to increase the

efficency and the life cycle of the ESU system Feasibility study of an ESU

Why Supercapacitors?The purpose is to allow higher accelerations and deceleration of the vehicle with minimal loss of energy, and conservation of the main battery pack.

IntroductionMotivations

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ObjectivesObjectives

IntroductionObjectives

Analysis and design of supercapacitor pack

Analysis and design of supercap equalization net Analysis and design of DC/DC converter Definition of a dynamic model for supercap and

DC/DC converter with several degrees of approximation

Design procedure definition for supercaps

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Battery vs SupercapBattery vs SupercapType

Energy/ weight [Wh/kg]

Power/Size

[W/kg]

Nom,Cell [V]

CyclesDurabilit

y[#cicli]

Charge time [h]

Lead (Pb) 20÷30 1÷300 2 200÷300 8÷16

Ni-Cd 30÷55 10÷900 1.25 1500 1

Ni-MH 50÷8020÷1000

1.2530÷500

2÷4

Li-ion110÷160

1800 3.7500÷1000

2÷4

Li-ion VHP Saft

74 6900 3.6 500000 20m

Nanosafe 90 4000 13.8 15000 <10m

Supercap 3.9÷5.7470÷13800

2.5÷2.7

1000000 0÷30s

The non conventional batteries have High Power density but the charging time is high for this application.

Supercapacitor

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SupercapacitorSupercapacitorADVANTAGES

High Capacitance and ultra low ESR

High Density of Power Fast charging /

discharging High Available Current High number of life

cycles

DRAWBACKS Low voltage for each

cell High Weight and

Volume Very expensive

Supercapacitor

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Equalization netEqualization net

The disparities among the cell's parameters won't exhibit the same charging dynamic and, at end of charge transient, some cells may present over-voltage while some others are insufficiently charged.

The tolerance of the supercaps is 20%, but presumably if you buy supercaps from the same stock the tolerance reduces itself.

This involves the introduction of a control.

In power applications, supercapacitors are used in stacks where many cells are connected in series or in parallel to obtain acceptable voltages and energy.

Supercapacitor

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Possible SolutionPossible Solution

DC/DC active solution Switched Resistor Integration Kit

ADVANTAGES : High efficency

DRAWBACKS : Several DC/DC converter The implementation of the hardware and its control is very costly.

ADVANTAGES : Simplest Solution

DRAWBACK : Power loss

ADVANTAGES : High efficency User friendly

DRAWBACK : Expensive 40$

Supercapacitor

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IndexIndex


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ESU with SupercapacitorsESU with Supercapacitors

ADVANTAGES In case of failure is always guaranteed connection between the battery and the inverter. During braking, the controller decides which energy source recharge. This power system allows acceleration and deceleration of the vehicle with minimal loss of energy and minimizes the stress of the batteries.

DRAWBACK We need to design a Bidirectional DC/DC converter.

ADVANTAGES Simple realization

DRAWBACKS Great stress for battery No longer battery life with high absorbed currents Long charging time Few charge-discharge cycles

ACTUAL SYSTEM PROPOSED SOLUTION

ESU with Supercapacitor

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SpecificationsSpecifications Ptraction = 22kW

Phase of Traction = 5 s

Phase of Braking = 10 s

Supercapacitor Add-on

ESU must be fault tolerant

Weight of ESU : less possible

Other important elements

Vbattery = 200V

Restriction of DC/DC converter


Specifications

Matlab Algorithm

Results SC bank

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Sizing supercapacitor bankSizing supercapacitor bank

To respect the energy constraints, the physical limits of supercapacitors and the restrictions imposed by the DC/DC converter must be considered.

In our analysis the following issues have been taken into account:

Supercapacitor working voltage

Restriction of the DC/DC converter


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Supercapacitor working voltageThe working voltage of the supercaps must be lower than nominal voltage in order to lengthen life expectation.

The aging processes of supercapacitors are mostly driven by temperature and cell voltage, which have an influence on the calendar life of the devices.

2,6V (96% of continuous voltage rating) was chosen because it is a voltage that ensures a sufficent life expectancy.


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Supercapacitor working voltage1,3V (50% of continuous voltage rating) was chosen because it is a voltage that ensures a sufficient input voltage to the DC/DC converter and keeps the ratio max-input / min-input near 2.The discharge voltage ratio d (in %) of the supercapacitors bank is defined as:

The DOD “Depth of Discharge” (in %) is then equal to:

This equation shows that, for a 50% DOD, the useful energy represents 75% of the maximun energy. Is inefficent to discharge the bank below 50% of its max voltage.

Then the Energy of Supercapacitor bank is given by the following equation:


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Restriction of the DC/DC converterRestriction of the DC/DC converter

The converter imposes constraints on the ratio between maximum input voltage and minimum input voltage, also between output voltage and input voltage.The restrictions refer to a non-isolated converter.


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ProcedureProcedure

specifications

datasheet

VinMAX

Vinmin

Constraints DC/DC

# SC in series=N

Initial condition

N=1

Needed

Energy

Repeat this procedure for all models and for 1<N<100 and Research the SC bank with minimum weight.

Add Module

Does the number of SC

in series respect the

costraint 5:1 ?

Add SC

Choose a model

Calculate the energy

of a module

NeededEnergy

>E_module ?

save data

processing

NO

YES

YES

NO

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Compromise Weight-EnergyCompromise Weight-EnergyResult:The best compromise between weight and energy considering all the constraints on supercap and DC / DC converter has been found through a Matlab algorithm.

# cell in series (module): 35 # module: 1 # total of supercap : 35 Input voltage range: 45,5÷91 V Weight : 11,19 kg Energy: 133087J 36,96Wh Power:26.62kW for 5s Volume : 9000 cm3

Model:BCAP 1500


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IndexIndex


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DC/DC Bidirectional ConverterDC/DC Bidirectional ConverterIt is necessary because the supercapacitors voltage (91V) is different in comparison to the DC BUS voltage (200V).

Weight application : less possible

Principle of Operation

Step-downPhase

Step-upPhase

Vin[V] 200 45.5-91

Vout[V] 91 200

Iout[A] 100 110

Pout[kW] 9.1 22

Max time phase [s]

10 5

Constraint of application

Constraints

DC/DC Converter

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Comparison isolated-non isolatedComparison isolated-non isolatedTwo main categories of bidirectional DC/DC converters can be envisaged for this task:

Isolated converters Full Bridge Tapped Boost

Non isolated converters Buck+Boost Multiphase

Buck+Boost Multiphase Full BridgeTapped Boost

Inductor Very heavy N but light heavy heavy

Trasformator none none yes Yes L couple

Diff.Control Middle(2sw) Hard(Nsw) Hard(8sw) Middle(2sw)

Efficiency high high low middle

DC/DC Converter

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Non isolated convertersNon isolated converters

ADVANTAGES: Simplest topology of the DC/DC converterDRAWBACKS: Excessive weight Complicated Inductor costruction

ADVANTAGES: The key principle of these converters is the output current sharing among several parallel channels.DRAWBACK: Interleaved strategy is very difficult.

A variant of the Buck+Boost solution is the Multiphase Converter.

DC/DC Converter

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IndexIndex


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ModelingModelingThe modeling is needed to allow you to enter the ESU designed in the system.

Virtual Prototype : Longitudinal dynamics model of the vehicle

Modeling

ESU ModelingPlant

ACU

Host

ICE

Electric motor

Power Module

ECU System

Battery

Supercap

DC/DC Converter

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SupercapSupercap

Laboratory TestSimulink Model

Analysis of results

Modeling

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DC/DC Converter + SupercapDC/DC Converter + Supercap

FIRST APPROXIMATIONAssumptions:

Linearity

No losses (DC/DC)

Equations :

Buck eq.

Boost eq.

SECOND APPROXIMATIONAssumptions:

No Linearity,

Losses (DC/DC)

Equations :

State Equations(L,C)

Modeling

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Models ComparisonModels Comparison

In the first approx are visible only the mean values. Very fast time simulation. Simulation Time(40s) : 0,001s In the second approx are visible the instantaneous values and you can see the voltage/current ripple. Very long time simulation Simulation Time(40s) : 30'

Comparison ParametersAssumptions for the buck phase (braking):

Static Simulations (fixed duty cycle) Iniatial SC Voltage:60V D = duty cycle = 40% T = Period = 20 us Simulation time : 40s

Modeling

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First vs Second approximationFirst vs Second approximation

If you need a fast simulation, and you do not want to see the transient then you can use the first approximation model. If you want to see the current and voltage ripples you can use the second approximation model, this model is the most similar to the electric model. For a more accurate comparison should have circuital simulations.

Speed Simulation

Accurancy

First Approx Very fast low

Second Approx Very slow high

Modeling

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Dynamic SimulationDynamic Simulation

In the figure you cansee the possible real behaviour of the first approximation model. Are visible the correct functioning of the system. Very fast time simulation. Simulation Time(100s): 0,001s

Real operating assumptions :Dynamic Simulations (First approximation model with control) Iniatial SC Voltage : 0VD = duty cycle = variable T = Period = 20 usSimulation time : 100sC/!D = Charge/!Discharge = '1', after 40 s '0'

Modeling

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IndexIndex

Introduction Supercapacitor ESU with Supercapacitors DC/DC Converter Modeling Results Conlusions

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ResultsResults

The choices made concerning the following four points:

Topology DC/DC Converter SC Bank Modeling

Results

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TopologyTopology

In this solution we need to design only one bidirectional DC/DC converter. Inserting an electronic switch in the converter it is possible to guarantee the safeness of the application. The number of the supercap bank is not extreme. The supercap bank is an add-on of the existing system.

DC/DC converter with high voltage battery pack

ResultsTopology

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Bidirectional DC/DC ConverterBidirectional DC/DC Converter

The components are commercially available more easily It is a direct converter then avoids losses related to the transformer

ResultsDC/DC Converter

Multiphase

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Results Supercapacitor bankResults Supercapacitor bank

Number of Scap = 35Type of Scap = BCAP1500Resulting Capacitance = 42,85FResulting ESR = 16,45mΩEnergy storage=133087 J 36,97WhVolume = 9000cm3

Cost Scaps = 2750 dollarsWeight Scaps = 11,19 KgEstimated weight DC/DC converter 22 KgMax weight battery = 20 KgEstimated weight ESU 53KgEstimated operating temperature -25 ÷ 70 °C

ResultsSC Bank

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ESU ModelESU Model

The first approximation model is a simple solution and has a short time simulation, in the future it will be placed in the Virtual Prototype.

It will be used to evaluate the performance of the vehicle with and without the use of the supercapacitors.

ResultsModeling

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IndexIndex


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ConclusionsConclusions Very high cost (Supercap + DC/DC Conv.) High weight and volume (Supercap + DC/DC

Conv.)

In conclusion, for the requested application, the resulting data are excessive in terms of weight and volume occupied.However, to confirm these conclusions, it would be interesting being able to perform tests, using the simulator. They will produce curves that may highlight the performance gap with and without the ESU.

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ConclusionsConclusions

The supercaps are suitable to be used either in buses, trains, trolley buses...

...or in high performance vehicles, such as sport cars and competition motorcycles.

ThanksThanks

Aniello Valentino – Francesco Villella

design and optimization of an esu for hybrid light vehicles with the use of supercapacitors...

Documents

introduction motivations

supercaps slide

contex esu

constraints dcdc

addon supercapacitors

esu system feasibility

energy recovery

needed energy